Method of flow detection using visible light sensitive phosphors



United States Patent 3,117 ,227 METHOD OF FLGW DETECTION USING VISIELELIGHT SENSITIVE PIIQSPHORS Isidore Pollack, Westminster, Calih,assignor, by mesne assignments, to Purex Corporation, Ltd, a corporationof California No Drawing. Filed Aug. 2, i960, er. No. 46,2i85 3 Claims.(Cl. 250-71) This invention relates to procedure for non-destructivetesting of bodies which may be composed of metal, ceramic, plastic, andthe like, to detect flaws and cracks in the surface of said bodies, andis particularly concerned with a novel method of fluorescent penetrantinspection employing visible light for activating the fluorescent dye.

In known penetrant inspection methods for rapid location and evaluationof surface flaws or cracks in parts, a penetrant composition containinga fluorescent dye and which will penetrate the openings of the surfacecracks or flaws in the part, is applied to the surface of the test body,and the excess penetrant composition is removed from the surface of thebody. A developer composition is then applied to the part surface. Suchdeveloper can be in the form of a light colored powder, which acts as awick and causes the liquid penetrant containing the fluorescent dyewhich was retained in the cracks or surface flaws, to be drawn up out ofthe surface defects by capillary action. The part is then exposed toinvisible fluorescigenous light, and the location of the surface flawsis revealed by the emission of visible light by the fluorescentpenetrant dye which is retained in the cracks or flaws after thepenetrant composition is removed from the surface of the part.

In such conventional fluorescent penetrant processes, a source ofsubstantially invisible fluorescigenous light, usually ultra-violet, isemployed for the excitation of the fluorescent dye to cause it to emitvisible light to thereby locate the cracks and flaws. Such light sourcesmay include mercury vapor discharge lamps, X-ray tubes and cathode raytubes.

The use of such invisible fluorescigenous light and the light sourcesemployed for its production, present certain serious problems. In thefirst place when for example, mercury vapor lamps are used, it isnecessary to employ light filters which are transparent to ultra violetand essentially opaque to visible light. Not only are such filters ofteninefficient for producing the proper fluorescigenous light to obtainmaximum contrast between the fluorescent penetrant dye and thesurrounding area of the test body, but such equipment and the operationthereof are relatively expensive.

Another serious disadvantage to the use of invisible fluorescigenouslight is that the inspection areas are of necessity highly confiningenclosures or booths constructed to shut out extraneous visible light,and thus present unpleasant working conditions from the standpoint ofthe highly confining oppressive working area, the heat produced by thefluorescigenous light source, and the poor ventilation of such areas.

It is an object of this invention to provide a fluorescent penetrantinspection process, which eliminates the use of invisible orsubstantially invisible light for irradiation, such as ultravioletlight, and the necessity of special light sources for producing suchlight.

3,117,227 Patented Jan. 7, 1964 Another object is the provision of afluorescent penetrant inspection process which requires only visiblelight for activation or excitation of the fluorescent penetrant dye, yetproduces bright fluorescence.

A still further object is to afford a process of the above typeemploying visible light, and which is controlled so that the fluorescentdye is activated to produce maximum fluorescence.

Yet another object is to provide a fluorescent penetrant inspectionprocess in which high contrast between the fluorescent penetrant dye andthe background is achieved.

Other objects and advantages will appear hereinafter.

According to the invention, I have found that if a fluorescent penetrantdye, which is characterized by having an activating wave length withinthe visible spectrum, is used in penetrant inspection of a test body,the fluorescent penetrant retained in the cracks and flaws can beexcited by exposure solely to visible light, to obtain excellentcontrast between the fluorescent dye indicator present in the flaws andcracks of the test body and its surrounding area. According to aparticular feature of the invention, best results are realized, in termsof brighter fluorescence of the penetrant dye and greater contrastbetween such fluorescence and the surrounding area of the test body, itsuch visible activating light contains light waves in the visiblespectrum having the predominant activating wave length for producingmaximum fluorescence at the fluorescent maximum wave length of theparticular dye employed. Preferably the visible light employed isfiltered to provide the required activating wave length.

The expression visible light or within the visible spectrum as employedherein is intended to denote wave lengths between about 4,000 A. andabout 7,500 A., generally considered to be the wave length range oflight to which the human eye is responsive or sensitive.

By activating wave length I mean that wave length which is within amajor absorption band in the visible spectrum shorter than the Stokesradiation, i.e., a major band in the fluorescent emission spectrum ofthe dye which is of longer wave length than that of said absorptionband.

By fluorescent maximum wave length I mean that wave length at themaximum of the band spectrum of the fluorescence which characterizes thevisible color of the fluorescent dye. It is to be recognized that theband has width and will include wave lengths shorter and longer than thesaid maximum.

According to the invention I irradiate the test body with light withinthe visible spectrum containing wave lengths shorter than the wavelengths which charactize the fluorescent color of the fluorescent dye,and I preferably employ a radiation intensity of the irradiating sourceand a concentration of dye in the penetrant composition, such that therelative brightness of the fluorescent emission is substantially greaterthan the relative brightness of the background illumination produced bythe irradiating light. This difference in brightness should be such thatunder inspection conditions there is a substantial contrast between theemitted fluorescence and the background light from the test body.

In one embodiment I select an intensity of the irradiating radiation anda concentration of the dye to produce substantially total absorption ofthe irradiating radiation so that the background appears matte black.

However, I may employ an intensity of irradiating radiation and/or dyeconcentration such that the relative brightness of the background issubstantially less than the relative brightness of the fluorescent dye.

I may also employ an irradiating radiation of such intensity and dyeconcentration that the background radiation is of an intensitysubstantially greater than that of the fluorescent radiation and, insuch case, I use a color separation between the irradiating radiationand the fluorescent radiation, e.g., by means of filters, which willselectively absorb the background light, and transmit the fluorescence.

The irradiation intensity and the concentration of fluorescent dye inthe penetrant composition are preferably adjusted to produce a desiredor maximum contrast between the fluorescent penetrant, at the locationof the cracks and flaws, and the background. For each individualinspector, these values may vary to some extent for achieving maximumcontrast. For example, if the background illumination is too great, theirradiating intensity may be reduced. It will also be understood thatthe optimum concentration of fluorescent dye employed will also dependon the particular dye utilized.

The invention process can be employed in connection with the use of alarge 'variety of fluorescent dyes, but preferably those which emit afluorescent color having wave lengths in the region ranging from greento red, and embracing, for example, fluorescent emittmg wave lengths ofabout 5,000 A. and greater.

Thus, for example, a yellow fluorescent penetrant dye emits radiation of5,400 A. This dye can be activated by energy within the range between3,500 and $700 However, I have found that it is possible to obtainmaximum fluorescent emission by using an activating wave length which issubstantially, although not necessarily, exclusively monochromatic, andwhich is in thC V1SlblC range of the spectrum. For this yellow dye,light of about 4,600 A., which is within the visible portion of thespectrum, gives good contrast and maximum fluorescence.

As is readily apparent, the instant process has the important advantageof eliminating the necessity for the use of invisible fluorescigenous orultra violet light to activate the fluorescent penetrant dye. Myprocessmakes it unnecessary to use the relatively expensive equipmentemployed as sources for such light, and significantly reduces the powercosts of the inspection procedure. These advantages are obtained withoutsacrifice of efficient activation of the fluorescent penetrant to obtaingood test results. Consequently, this technique el1minates the almostintolerable working conditions heretofore encountered by the inspectors,in avoiding the necessity for confined poorly ventilated enclosed testbooths, and permits inspection under normal working conditions. Thus,for example, in the instant process, an ordinary tungsten lamp may beemployed by screening its emission of substantially all wave lengthsexcept the visible activating wave lengths including that required formaximum fluorescence from the fluorescent penetrant dye, according tothe invention. Hence, in the specific example noted above, a tungstenlamp may be employed as a light source for irradiating the yellow dye,by placing over the lamp a suitable filter which has a maximumtransmission at the visible approximately 4,600 A. required for maximumactivation of the dye to provide maximum fluorescence. Such a filter maybe one which transmits in the range of about 4,500 to about 4,700 A.,with a maximum transmission at about 4,600 A.

In addition, the instant process is rendered more sensitive and pleasingto the eye, where the operator utilizes a pair of eyeglasses tinted withthe color of the fluorescent dye or employs a suitable filter forviewing. Thus, in connection with the specific example of the use of ayellow fluorescent penetrant dye as above described, if the operatoremploys a pair of glasses tinted with a yellow dye or with a filtertransmitting only yellow, this renders the surrounding background of thetest body a matte black and intensifies the yellow fluorescence of thepenetrant dye. Other filters may be utilized, if desired, to change theappearance and background of the test body without substantiallyaltering the brightnes or contrast of the fluorescence produced by thefluorescent penetrant dye.

The penetrant composition employed in my invention may comprise aconventional solvent vehicle within which the fluorescent dye issoluble. The penetrant vehicle should be a liquid which is itselfsubstantially nonfluorescent and having good wetting properties and theability to penetrate fine surface cracks and imperfections readily.Satisfactory penetrant vehicles include, for example, petroleumsolvents, kerosene, a mineral oil or spirit, or mixtures thereof, lightfuel oils, and the like. Solvent vehicles found suitable may comprise,for example, a mixture of tributyl phosphate and toluene. Other solventsinclude, for example, ketones, esters and organic acids. The penetrantmay also contain anemulsifying agent which renders the penetrantcomposition water emulsifiable. Such emulsifying agents may be, forexample, oil-soluble soaps, detergents, and the like. The amount offluorescent dye incorporated in the penetrant composition may range fromabout 0.05 to about 2.5%, preferably from about 0.1 to about 1.5%, byweight of such composition.

The dye penetrant composition is maintained on the surface of the partfor a period suflicient to permit the composition to penetrate thecracks and imperfections in the part surface, e.g. for about 5 to 30minutes.

The penetrant composition is then removed or washed oil the surface ofthe part being tested, without being removed from the openings of thesurface cracks or flaws. This is accomplished by wiping with a cloth, ora solvent impregnated cloth, or with water where the penetrantcomposition has been rendered water-emulsifiable by addition thereto ofan emulsifying agent, or by a post emulsifying agent where noemulsifying agent has been added to the penetrant composition itself.Such emulsifying agents may be, for example, oil soluble soaps,detergents, wetting agents, or the like, e.g. an al-kyl aryl sulfonateor an alkyl aryl polyether alcohol.

The part is preferably then sprayed with a developer composition. Suchdeveloper may be a dry developer which contains chalk, talc, silicaaerogel, diatomaceous eartih, silica, a mixture of silica and talc, orother fine absorbent powdery material such as calcium or magnesiumcarbonate. Wet developers can also be used, in which a power such astalc or calcium carbonate in an amount ranging from about 2 to about30%, e.g. about 12%, by weight, is suspended in a vehicle consisting,for example, of ethanol, isopropanol or any other aliphatic alcohol, achlorinated hydrocarbon, or other sufiiciently volatile hydrocarbon. Ifdesired, pigmentsv or dyes such as a phthalocy-anine dye of which one ofthe Heliogens is an example, may be incorporated in the developercomposition, preferably producing a color, e.g. blue, which is incontrast with the color, e.g. yellow, of the fluorescent penetrant dye.When using a wet developer, such developer is allowed to dry, afterapplication to the part surface, to form a continuous coating thereon.

The powdery material of the developing agent absorbs the penetrant andfluorescent dye therein, contained in the cracks and flaws of the partsurface, by capillary action and forms a fluorescent smear adjacent thecrack openings.

-While it is preferred to apply a developer in accordance with theprocedure set forth above, this step is not essential for obtaining theimproved results of my in vention. In the event that the developer isnot used, flaw or cnack indication is not as vivid as when this step isused. However, for certain applications the decreased sensitivity may betolerated or indicated because of increased economies of inspection andthe lack of necessity for determining the location of surface flaws ofsufficiently small size as not to impair the function of the part undertest.

In either case the test part is then exposed to visible light accordingto the invention to obtain maximum fluorescence of the penetrant dye.

The following examples illustrate practice of my invention:

Example 1 A dye penetriant composition is prepared as follows:

ercent by weight Calcofluor Yellow HEB, Color Index, FluorescentBrightening Agent No. 4 0.6 SAE No. 30 lubricating oil 30.0 Tributylphosphate 69.4

The above penetrant composition is applied to the surface of a metaltest body and maintained thereon for from 5 to 30 minutes, and thesurface is then wiped clean of excess penetrant, or cleaned withStoddard solvent or by use of an emulsifier composition as follows:

Percent by weight Light mineral oil 30.0

A developer having the following composition is then sprayed on the partsurface.

Percent by weight Diatomaceous earth 90.0

Silica aerogel 10.0

Alternatively a liquid developer of the following composition can beemployed:

Percent by weight Calcium carbonate 10.0

Ethanol 90.0

The test body surface including the cracks and defects therein, isexposed to visible blue light of wave length about 4,400 A. Such lightis provided by 'an ordinary tungsten lamp over which is placed a filterhaving a maximum transmission generally corresponding to the predominantactivating wave length of Oallcofluor Yellow HEB for producing maximumfluorescence that is, 4,400 A. Such filter may be a Oo-rning C.S.-5-75or a Bausch and Lomb filter No. 33-78-44, having a maximum transmissionat 4,650 A. The cracks and flaws in the test body are revealed at thelocation of the bright yellow fluorescence produced by the penetrant dyein the mouth of such cracks and flaws, on exposure to such visible bluelight.

Example 2 Rhodamine 6 GDN, Color Index 45160 0.5 Toluene 69.5 Tributylphosphate 30.0

The penetrant composition is applied to a test body, the excesspenetrant removed fro-m the part surface by an emulsifier and adeveloper composition is applied to the surface, employing an emulsifierand a developer as described in Example 1. The part is then exposed toyellow light by means of an ordinary tungsten lamp, over which is placeda filter such as a B-ausch and Lomb No. 33-78-52, having a peaktransmittance at 5,200 A. corresponding to the predominant activatingwave length for maximum fluorescence at about 5,500 A. of the penetrantdye to produce a greenish yellow fluorescence at the locations of thepenetrant dye in the cracks and flaws.

6 Example 3 The procedure of Example 1 is repeated through applicationof the developer, employing in place of the penetrant composition ofExample 1 the following:

Percent by weight Uranine S.W.S., Color Index, Acid Yellow 73 1.0 Ethylalcohol 99.0

The developed part is then irradiated using an ordinary tungsten lampover which is placed a suitable filter such as Bausch and Lomb No.33-78-46 which transmits light of the predominant activating wave lengthof about 4,500 A. to obtain maximum fluorescence of the dye at about5,200 A., producing a greenish yellow fluorescence at the cracks andflaws in the part surface.

Example 4 The procedure of Example 1 is repeated, but employing in placeof Oalcofluor Yellow HEB in the penetrant, the respective fluorescentdyes listed in the table below. In each case :an ordinary tungsten lampis employed for irradiating the developed test body, employing asuitable filter to transmit light at the predominant activating wavelength for obtaining maximum fluorescence for each of the dyes. Thevalues of such predominant activating and maximum fluorescence wavelengths for the respective dyes, the type of filter employed in eachinstance, and the fluorescent color of each of the dyes produced at thelocation of the cracks and imperfections of the test body, are alsolisted in the table below.

Predom- Fluorescent mating Maximum Fluo- Fluoreseent Dye Activating WaveFilter rescent Wave Length, A. Color Length, A.

Rhodamine B, Color 5, 500 6,000 Bausch & Red.

Index 45,170. omb

Eosinc G. Color Index 5, 250 5, 800 Bauseh & Greenish 45,380. Lomb Yel33-78- low. 52. Auramine, Color 4, 600 5, 200 Bausch & D0.

Index 41,000. Lomb 33-78- 46. Fluoral 7GA, Color 4, 600 5, do D0.

Index-Fluorescent brightening agent 75. Azosol Brilliant Yel- 4, 600 5,100 do Do.

low GGF, Color Inilfx-SOlWIli; Yellow Brilliant Yellow 6G 4, 000 5, 100do D0.

Base, Color Index- Solvent Yellow 44.

From the foregoing, it is seen that the invention provides a simplemeans employing visible light produced by common inexpensive lightsources, for irradiating fluorescent penetrant dyes in penetrmtinspection methods, such visible light being selected preferably of awave length corresponding to the predominant maximum activating wavelength to obtain maximum fluorescence for the panticular dye employed. Afurther important advantage of the instant invention is that it permitsinspection of test bodies to be carried out in relatively open workspaces, avoiding the cramped, poorly ventilated and oppressive enclosedinspection booths heretofore required for inspection employingfiuorescigenous light.

While I have described particular embodiments of my invention for thepurpose of illustration, it should be understood that variousmodifications and adaptations thereof may be made within the spirit ofthe invention as set forth in the appended claims.

I claim:

1. The method for inspecting bodies for cracks and flaws, comprisingapplying a fluorescent penetrant dye composition containing afluorescent dye to a test body,

said fluorescent dye having a predominant activating wave length forproducing maximum fluorescence, within the visible spectrum, permittingsaid penetrant to remain on the test body for a period sufficient tocause said penetrant to enter cracks and flaws on the surface of saidbody, removing excess penetrant composition from the surface of saidtest body, applying a developing composition containing an absorbentpowder to said test body, and inspecting such body solely under lightwaves inthe visible spectrum having a wave length corresponding to thepredominant activating wave length for producing maximum fluorescence ofsaid fluorescent dye, and producing a fluorescent emission from saidfluorescent dye.

2. The method for inspecting bodies for cnacks and flaws, comprisingapplying a fluorescent penetnant dye composition containing a yellowfluorescent dye to a test body, said fluorescent dye having anactivating wave length for producing fluorescence, within the visiblespectrum, permitting said penetrant to remain on the test body for aperiod suflicient to cause said penetnant to enter cracks and flaws onthe surface of said body, removing excess penetrant composition from thesurface of said test body, applying a developing composition containingan absorbent powder to said test body, and inspecting such body solelyunder visible light containing light waves in the visible spectrumhaving a wave length corresponding to the activating wave length of saidyellow fluorescent dye, and producing a fluorescent emission from saidfluorescent dye.

3. The method for inspecting bodies for cracks and flaws, comprisingapplying a fluorescent penetrant dye composition containing a yellowfluorescent dye to a test body, said fluorescent dye having apredominant activating wave length for producing mmimum fluorescence,Within the visible spectrum, permitting said penetrant to remain on thetest body for a period suficient to cause said penletnant to entercracks and flaws on the surfam of said body, removing excess penetrantcomposition from the surface of said test body, applying a developingcomposition containing an absorbent powder to said test body, andinspecting such body solely under light waves in the visible spectrumhaving a wave length corresponding to the predominant activating wavelength for producing maximum fluorescence of said yellow fluorescentdye, and producing a fluorescent emission from said fluorescent dye.

4. In a method for inspecting bodies for cracks and flaws, including thesteps of applying a penetrant composition to a test body and removingexcess penetrant from the test body, the improvement which comprisesincorporating in said penetrant a fluorescent dye having an activatingwave length for producing maximum fluorescence, within the visiblespectrum, and irradiating said test body solely with light waves in thevisible spectrum having a wave length corresponding to the predominantactivating wave length for producing maximum fluorescence of saidfluorescent dye, and producing a fluorescent emission from saidfluorescent dye, the intensity of said visible light and theconcentration of said fluorescent dye being such that a substantialcontrast is obtained between the emitted fluorescence and the backgroundlight from the test body.

5. The method for inspecting bodies for cracks and flaws, comp-risingapplying a fluorescent penetnant dye composition containing afluorescent dye to a test body, said fluorescent dye having apredominant activating wave length for producing maximum fluorescence,within the visible spectrum, permitting said penetnant to remain on thetest body for a period sufficient to cause said penetrant to entercracks and flaws on the surface of said body, applying an emulsifier forsaid penetrant composition to said surface to remove excess penetrantcomposition from said surface, applying a developing compositioncontaining an absorbent powder to said test body, and inspecting suchbody solely under light waves in the visible spectrum 8. having a Wavelength corresponding to the predominant activating wavelength forproducing maximum fluorescence of said fluorescent dye, and producing afluorescent emission from said fluorescent dye.

6. The method for inspecting bodies for cracks and flaws, comprisingapplying a fluorescent penetnant dye composition containing afluorescent dye to a test body, said fluorescent dye having apredominant activating wave length for producing maximum fluorescence,within the visible spectrum, permitting said penetrant to remain on thetest body for a period suflicient to cause said penetuant to entercracks and flaws on the surface of said body, removing excess penetrantcomposition from the surf-ace of said test body, applying a developingcomposition con,- taining an absorbent powder to said test body, andirradiating said body solely with light from a tungsten lamp sourcefiltered to emit solely light waves in the visible spectrum having awave length corresponding to the predominant activating wave length forproducing maximum fluorescence of said fluorescent dye, and producing afluorescent emission from said fluorescent dye, the intensity of saidvisible light and the concentration of said fluorescent dye being suchthat a substantial contrast is obtained between the emitted fluorescenceand the background light from the test body.

'7. The method for inspecting bodies for cracks and flaws, comprisingapplying a fluorescent penetrant dye composition containing a yellowfluorescent dye to a test body, said fluorescent dye having apredominant activating Wave length for producing maximum fluorescence,within the visible spectrum, permitting said penetrant to remain on thetest body for a period sumcient to cause said penetnant to enter cracksand flaws on the surface of said body, removing excess penetnantcomposition from the surface of said test body, applying a developingcomposition containing an absorbent powder to said test body,

. and irradiating said body solely with light from a tungsten lampsource filtered to emit solely blue light having a wave lengthcorresponding to the predominant activating wave length fior producingmaximum fluorescence of said yellow fluorescent dye, and producing afluorescent emission from said fluorescent dye, the intensity of saidvisible light and the concentration of said fluorescent dye being suchthat a substantial contrast is obtained between the emitted fluorescenceand the background light from the test body.

8. The method for inspecting bodies for cracks and flaws, comprisingapplying a fluorescent penetrant dye composition containing afluorescent dye to a test body, said fluorescent dye having apredominant activating wave length for producing maximum fluorescence,within the visible spectrum, permitting said penetrant to remain on thetest body for a period suflicient to cause said penetrant to entercracks and flaws on the surlia'ce of said body, removing excesspenetrant composition from the surface of said test body, and inspectingsuch body solely under light Waves in the visible spectrum having a wavelength corresponding to the predominant activating wave length forproducing maximum fluorescence of said fluorescent dye, and producing afluorescent emission from said fluorescent dye.

References Cited in the file of this patent UNITED STATES PATENTS2,478,951 Stokely Aug. 16, 1949 2,636,127 De Forest et al Apr. 21, 19532,920,203 Switzer et al. Jan. 5, 1960 2,953,530 Switzer Sept. 20, 19603,028,338 Parker Apr. 3, 1962 OTHER REFERENCES Luminescence of Solids ofLeverenz, John Wiley & Sons, Inc, New York, 1950, Table 5 (between pages72 and 73).

1. THE METHOD OF INSPECTING BODIES FOR CRACKS AND FLAWS, COMPRISINGAPPLYING A FLUORESCENT PENETRANT DYE COMPOSITION CONTAINING AFLUORESCENT DYE TO A TEST BODY, SAID FLUORESCENT DYE HAVING A PREDOMINATACTIVATING WAVE LENGTH FOR PRODUCING MAXIMUM FLUORESCENCE, WITHIN THEVISIBLE SPECTRUM, PERMITTING SAID PENETRANT TO REMAIN ON THE TEST BODYFOR A PERIOD SUFFICIENT TO CAUSE PENETRANT TO ENTER CRACKS AND FLAWS ONTHE SURFACE OF SAID BODY, REMOVING EXCESS PENETRANT COMPOSITION FROM THESURFACE OF SAID TEST BODY, APPLYING A DEVELOPING COMPOSITION CONTAININGAN ABSORBENT POWDER TO SAID TEST BODY, AND INSPECTING SUCH BODY SOLELYUNDER LIGHT WAVES IN THE VISIBLE SPECTRUM HAVING A WAVE LENGTHCORRESPONDING TO THE PREDOMINANT ACTIVATING WAVE LENGTH FOR PRODUCINGMAXIMUM FLUORESCENCE OF SAID FLUORESCENT DYE, AND PRODUCING AFLUORESCENT EMISSION FROM SAID FLUORESCENT DYE.